Sancho had to contend with Castilian irredentism and Aragonese ambition. His act of persuading the Moorish king of Saragossa to become his vassal offended Alfonso VI of Castile, who invaded Pamplona (1074) and conspired with Sancho’s brothers and magnates to assassinate him at Peñalén. The kingdom of Pamplona was then occupied by Sancho Ramírez of Aragon, with Navarrese approval.